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Comment by OJFord | Hacker News Reader

I think this overcomplicates the flaw, a very simple way of looking at it is that muscle has approx 5x the density of fat.

So if you take someone (or two people) slim, small frame, and compare them piling on muscle vs. fat, the former is obviously healthier, and yet will see them be 'overweight' per BMI far sooner.

I don't have any clinical experience, IANAD, so take with mountains of salt etc., but I'd have thought a simple change that would go a long way would be to have say three BMI ranges instead of one (well, for a given country anyway!) categorised by eye-balling or self-reporting.

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It is much harder to measure muscle mass at home, or even at the doctors office. Different methods show very different results when people are measured at the same time.

We need a simple proxy method for estimating the healthy weight range.

I didn't suggest measuring muscle mass, I said you could categorise a person (or yourself) into one of say three BMI ranges according to whether you were small/mid/big 'build'.

Obviously not as good as actually measuring muscle mass, or anything more scientific, but I think it would be a pretty trivial way of making the BMI estimate another chunk better.

The guy who's average day involves no movement, and then a cheeseburger and milkshake for lunch before talking with his bros as the gym and then coming home for a few cold brewskis is convinced he's got one of those "big" builds you're talking about and that standard BMI doesn't apply to him. He's only imaginary, but I'm pretty sure he's wrong.

The assessment you're trying to make just isn't reliable.

Muscle is about 15% more dense than fat.

I agree, but eye-balling and self reporting is too subjective. In some countries you get priority in the covid-19 vaccination line if you have a high BMI because it was correlated to deaths.

Perhaps add another variable like volume to distinguish fat and muscle (measured as Archimedes in a bathtub), but as you notice it break the reason that makes BMI so popular. From the article:

> “BMI doesn’t cost anything — it’s cheap and quick,”

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